Transversely or sidewardly extending, elongate headers of from about 12 feet to 30 feet and greater in length are commonly utilized on windrowing machines for cutting and windrowing crops such as cereal grains and other seed crops, as well as grasses. Historically, the headers rested on skid shoes which moved along the surface of a field or pasture, to position cutting apparatus of the header, such as an elongate sickle cutter bar or a row of disk cutters, close to the surface for cutting the stalks or stems of crops and grasses close to the surface.
More recently, it has become more desirable and customary to cut the stalks of crops higher than is possible with the header resting on skid shoes. Prior known models of windrowers used hydraulic cylinders to carry the header at the desired height with flotation springs carrying a major percentage of the header weight. Newer generations of windrowers use hydraulic cylinders and accumulators to lift the header and also provide header flotation when the header is lowered to the ground in a cutting mode. Such newer generation windrowers have been found to be efficient for cutting hay crops, but some have no provision for carrying the header above the ground while also providing a flotation capability. A flotation capability is desirable on a header carried off the ground to allow the header to be guided over obstacles and uneven ground without damaging the cutting apparatus of the header.
A settable sideward tilt capability has also been found to be a desirable feature, as it allows for accommodating uneven terrains such as where one side of a swath of a field or pasture to be cut is higher than the other. It may also be desirable to leave stubble on a field or pasture cut at an angle so as to retain more driven snow for better moisture retention when the snow melts. Similarly, in some circumstances it can be desirable to have the capability to independently raise and lower the ends of a header to correct for undesired sideward or transverse tilt. And, in many instances, it is desirable to have the capability to easily return to an earlier selected cut height, and tilt, after lifting of the header.
It has also been found that controlling of the lateral orientation of the header, whether a level or tilted orientation, when using a height control system is dependent upon the system being able to maintain an even header position during the raise and lower operations. For example, when using wider headers, such as a draper type header, which can be up to 36 feet wide, precise control over left and right lift arm movement is desired because small changes in lift arm position create greater height changes at the ends of the header. Likewise a greater precision is required on counterbalance when using a parallel circuit type lift system wherein the lift cylinders are jointly connected in parallel to the pressurized fluid source. Because of the parallel connection of the cylinders, a shortcoming that has been observed is that the dynamic forces generated during spin turns at the end of a cut or swath can cause the header to lean, even if the header is not being raised during the turn. These same forces generated during spin turns at the end of a cut or swath are a particular problem when using a wider header, as they have been observed to cause the wider header to lean if the header is being raised during the turn.
Thus, what is sought is a header height control system and apparatus for a work machine such as an agricultural windrowing machine or a harvesting machine, which provides a height control capability in combination with a float capability and a sideward or transverse tilt capability, along with a return to previously selected cut height capability, and which otherwise overcomes one or more of the shortcomings and limitations set forth above.